HSC 2012-2015 Chemistry Marathon (archive) (5 Viewers)

[kawaiipotato]

re: HSC Chemistry Marathon Archive

ive been doing bio since last tuesday that i've forgotten some chemistry.

Need to sharpen up:

"

In dotpoints:
- From t = 0 to t = 4, the system is at equilibrium (constant molarities)
- At t = 4, the reaction was heated. By Le Chatelier's Principle, the system will shift towards the endothermic reaction, that is, the forward reaction. This causes the concentrations of reactants to decrease and the concentration of products to increase as the system attempts to return to equilibrium. (t = 4 to t = 10) shown by the curvature of the graph
- At t = 10, the sudden decrease in [CO] indicates that CO was removed from the system. This removal of CO will cause the equilibrium to shift (stated by LCP), right, further decreasing the concentration of reactants and increasing the concentration of products as it tries to return to equilibrium.
-At t = 14, as both [reactants] and [products] changed, this indicates a volume change and thus a pressure change. The increase in volume caused the [reactants] and [products] to decrease. By LCP, the equilibrium shifts towards the more gaseous moles reaction thus causing the graph to show an increase in [products] and a decrease in [reactants]
note: the shifting all happens according to the mole ratio which is 1:1:1

 

[kawaiipotato]

re: HSC Chemistry Marathon Archive

Yeah I do Industrial haha, I probably should have put concentrated acetic acid or something along the lines of that

If it's concentrated, there would be little amount of ionisable [H+] so wouldn't adding water cause the 'burning' sensation from acids to start occuring, (giving the acid opportunity to ionise) until it's diluted enough?

 

[Ekman]

re: HSC Chemistry Marathon Archive

Assess the use of vinegar in this video (2 marks)

(Question was inspired by Crisium)

 

[Librah]

re: HSC Chemistry Marathon Archive

Explain with relevant dank chemical equations, why Librah is so amazing. (55 marks)

 

[InteGrand]

re: HSC Chemistry Marathon Archive

Explain with relevant dank chemical equations, why Librah is so amazing. (55 marks)

What is the marking criteria?

 

[Speed6]

re: HSC Chemistry Marathon Archive

I actually cared to memorise the periodic table when I was in Year 10 in atomic number order. This question is so troll though Speed; you get a periodic table in the exam!

Yeah I know you do, complete troll question.

Band...6......

https://youtu.be/zFy5rZcN5ks

https://youtu.be/S-mFkx7ReVY

The proof is here, can't question you at all. Well done man.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Explain with relevant dank chemical equations, why Librah is so amazing. (55 marks)

I think this was the 2069 HSC Band 6 decider...

 

[Librah]

re: HSC Chemistry Marathon Archive

I think this was the 2069 HSC Band 6 decider...

You know your history.

What is the marking criteria?

Must praise Librah

 

[leehuan]

re: HSC Chemistry Marathon Archive

I seriously need a definitive answer for this so I am going to have to link this post...


http://community.boredofstudies.org...chemistry/343863/making-soaps-laboratory.html

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

The measured potential difference obtained from a galvanic cell varied from the theoretical value.
Outline steps the student could have taken to minimise this variation. 2 MARKS

 

[rand_althor]

re: HSC Chemistry Marathon Archive

The measured potential difference obtained from a galvanic cell varied from the theoretical value.
Outline steps the student could have taken to minimise this variation. 2 MARKS

Ensure electrolytes are 1M, and conditions are 25 degrees/100kPa. Clean the electrodes too.

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

Here is a 7 marker. Feel free to answer in dot point form so it takes quicker.

 

[aanthnnyyy]

Chemistry marathon 2015

Here is a 7 marker. Feel free to answer in dot point form so it takes quicker.

1) Glucose -> Mixture of Ethanol
- fermentation of glucose through bio catalyst yeast @37 deg and exclusion of air with products ethanol and co2 gas (c6h12o6 -> 2c2h5oh +2co2)

2) once ethanol 14-15% concentration yeast cannot survive; ethanol is distilled to remove co2 and obtain pure ethanol

3) pure ethanol then undergoes esterification reaction with butanoic acid under Reflux involving a condenso, boiling chips to reduce volatility + allow to be performed at long periods of time at high temperatures (diagram). Drops of concentrated h2so4 also used to act as a dehydrating agent. (Include reaction here)

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

1) Glucose -> Mixture of Ethanol
- fermentation of glucose through bio catalyst yeast @37 deg and exclusion of air with products ethanol and co2 gas (c6h12o6 -> 2c2h5oh +2co2)

2) once ethanol 14-15% concentration yeast cannot survive; ethanol is distilled to remove co2 and obtain pure ethanol

3) pure ethanol then undergoes esterification reaction with butanoic acid under Reflux involving a condenso, boiling chips to reduce volatility + allow to be performed at long periods of time at high temperatures (diagram). Drops of concentrated h2so4 also used to act as a dehydrating agent. (Include reaction here)

yep pretty much..obviously you would go more into depth for each though if you weren't writing dot point.

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

Discuss how buffers are used in natural systems with a named example. 4 MARKS

 

[Crisium]

re: HSC Chemistry Marathon Archive

Example of Saponification:

Glycerol + Stearic Acid ---> Glyceryl Tristearate + Water

Glyceryl Tristearate + Sodium Hydroxide ---> Sodium Stearate + Glycerol

So in a way, is glycerol being regenerated?

 

[Chris_S]

re: HSC Chemistry Marathon Archive

ive been doing bio since last tuesday that i've forgotten some chemistry.

Need to sharpen up:

"

This was in my trial paper lol.

 

[Speed6]

re: HSC Chemistry Marathon Archive

Discuss how buffers are used in natural systems with a named example. 4 MARKS

After this question has been answered, I would like the 2015'ers to try this question:

Assess the potential of ethanol as an alternative car fuel, or as an additive to petrol, and discuss advantages and disadvantages of its use. (7 marks)

 

[Crisium]

re: HSC Chemistry Marathon Archive

After this question has been answered, I would like the 2015'ers to try this question:

Assess the potential of ethanol as an alternative car fuel, or as an additive to petrol, and discuss advantages and disadvantages of its use. (7 marks)

I don't think anyone will be willing to do it haha

By the time you do your HSC you would have encountered the same question plenty of times

 

[Anousha]

re: HSC Chemistry Marathon Archive

After this question has been answered, I would like the 2015'ers to try this question:

Assess the potential of ethanol as an alternative car fuel, or as an additive to petrol, and discuss advantages and disadvantages of its use. (7 marks)

I have a feeling a similar question will be in the exam this year.. did it to refresh my memory haha

Ethanol is a versatile solvent that has many adv and disd.
Advantages-
- Ethanol as a renewable fuel: ethanol is produced from renewable sources (fermentation of biomass), whereas other fuels are produced from petroleum (C61206 -> 2C02 + 2H20 (on top of arrow 37C, yeast, airlock))
- Net Co2 stays constant: the amount of Co2 produced in heat of combustion (C2H5OH + 302 -> 2CO2 + 3H20 ) the same amount is required to grow crops for ethanol ( photosynthesis for ethanol crop growth: 6CO2 + 6H20 -> C61206 + 602)
-10-15% of ethanol safely added to petrol w/o any modifications and causing damage to engines. (wouldn't need to be distilled) = reduces costs

Disadvantages-
- existing car engines need to be modified if more than 10-15% ethanol is used, distillation is energy intensive = economic pressures + high costs involved
- ethanol has a lower heat of combustion than petrol: combustion of ethanol produces less energy than same amount of octane, car can travel further with same amount of octane thus ethanols expensive
- large areas of land is needed to grow crops for ethanol (later used for fermenting) this is a problem as land is needed to grow food crops and land clearance contributes to salinity, deforestation, soil erosion, impacts on living organisms/environment.

Overall, ethanol has great potential as an alternative car fuel as it is renewable and biodegradable than can be safely added to petrol (10-15%) w/o any modifications.